Recently, memory capacity of a NAND flash memory has increased, and the number of word lines in one chip has also increased.
In writing of data, an error in part of bits in one page selected by one word line can be corrected by using an error correction code (ECC). However, it is difficult to correct an error or omission in data in units of pages by using an ECC.
Accordingly, heretofore, in order to protect data in units of pages, data identical to the data to be written is written to an area different from the data to be written to thereby prepare a backup.
However, in order to record identical data such as the backup in a different area, it is necessary to write the identical data twice, and hence extra time has been required to write data, and the system throughput has been lowered. Thus, for this reason, a memory system enabling data to be written securely at high speed is desired.